Additive composition for lubricating oil

ABSTRACT

An additive composition is provided for a lubricating oil that is easy to produce, does not have adverse effects, such as causing rubber seals to swell, and is excellent in storage stability. The additive composition contains a metal salt of a phosphorus-containing compound represented by formula (1) in an amount of 10 to 90 percent by mass of the composition, contained in a hydrocarbon solvent selected from a mineral oil, a hydrocarbon synthetic oil and a mixture thereof, the hydrocarbon solvent having a 100° C. kinematic viscosity of 0.5 to 4.5 mm 2 /s, a % C A  of 3 or less, and a sulfur content of 0.05 percent by mass or less: 
     
       
         
         
             
             
         
       
         
         
           
             wherein X 1  and X 2  are each independently oxygen or sulfur, R 1 , R 2 , R 3 , and R 4  are each independently a straight-chain alkyl group having 3 to 12 carbon atoms, the average of the carbon number is 5 or greater, and M is a divalent metal atom.

TECHNICAL FIELD

The present invention relates to additive compositions containing a metal salt of a phosphorus-containing compound for lubricating oils.

BACKGROUND ART

Metal salts of phosphorus-containing compounds such as dialkylthiophosphoric acid esters, dialkylphosphoric acid esters or the like, which are solids or viscous liquids at ambient temperatures have problems that they are poor in handleability during the production and transportation thereof, cannot be dissolved in a base oil kept at ambient temperature, or are poor in storage stability after being dissolved. A technology has been, therefore, proposed wherein such metal salts are dissolved in an amine compound or the like beforehand to be liquefied (see Patent Literature 1 below). However, since addition of a metal salt of a phosphorus-containing compound having been dissolved in such an amine compound to a lubricating oil would lead to adverse effects such as causing rubber seals to swell, the use of the metal salt are restricted to a large extent.

CITATION LIST Patent Literature

-   Patent Literature 1: WO2004/003118

SUMMARY OF INVENTION Technical Problem

The present invention provides an additive composition for a lubricating oil that does not give adverse effects such as causing rubber seals to swell, is excellent in storage stability and contains a metal salt of a dialkylthiophosphoric acid ester or a dialkylphosphoric acid ester that and is solid or viscous liquid at ambient temperatures, in a dissolved state and also a process for producing an additive composition for a lubricating oil comprising dissolving the above-mentioned compound in a base oil at a relatively low temperature of 60° or lower for a short period of time.

Solution to Problem

As the results of the extensive studies and research conducted by the inventors, the present invention has been accomplished on the basis of the finding that the use of a specific hydrocarbon solvent enables a metal salt of a phosphorus-containing compound to dissolve at a high concentration and a relatively low temperature of 60° C. or lower and the dissolved metal salt is excellent in storage stability.

That is, the present invention relates to an additive composition for a lubricating oil, comprising a metal salt of a phosphorus-containing compound represented by formula (1) in an amount of 10 to 90 percent by mass on the basis of the composition, contained in a hydrocarbon solvent selected from a mineral oil, a hydrocarbon synthetic oil and a mixture thereof, the hydrocarbon solvent having a 100° C. kinematic viscosity of 005 to 4.5 mm²/s, a % C_(A) of 3 or less, and a sulfur content of 0.05 percent by mass or less:

wherein X¹ and X² are each independently oxygen or sulfur, R¹, R², R³, and R⁴ are each independently a straight-chain alkyl group having 3 to 12 carbon atoms, the average of the carbon number is 5 or greater, and M is a divalent metal atom.

The present invention also relates to a process for producing an additive composition for a lubricating oil, comprising dissolving a metal salt of a phosphorus-containing compound represented by formula (1) in an amount of 10 to 90 percent by mass on the basis of the composition in a hydrocarbon solvent selected from a mineral oil, a hydrocarbon synthetic oil and a mixture thereof, the hydrocarbon solvent having a 100° C. kinematic viscosity of 0.5 to 4.5 mm²/s, a % C_(A) of 3 or less, and a sulfur content of 0.05 percent by mass or less:

wherein X¹ and X² are each independently oxygen or sulfur, R¹, R², R³, and R⁴ are each a straight-chain alkyl group having 3 to 12 carbon atoms, the average of the carbon number is 5 or greater, and M is a divalent metal atom.

The present invention also relates to a lubricating oil composition comprising the foregoing additive composition.

Advantageous Effects of Invention

The additive composition for a lubricating oil of the present invention can be produced at a relative low temperature that is 60° C. or lower for a short period of time, does not have adverse effects such as causing rubber seals to swell, and is excellent in storage stability.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more details below.

The hydrocarbon solvent used in the lubricating oil additive composition of the present invention is a solvent selected from a mineral oil, a hydrocarbon synthetic oil, and a mixture thereof, having a 100° C. kinematic viscosity of 0.5 to 4.5 mm²/s, a % C_(A) of 3 or less, and a sulfur content of 0.05 percent by mass or less.

Specific examples of the mineral base oil include those which can be produced by subjecting a lubricating oil fraction produced by vacuum-distilling an atmospheric distillation bottom oil resulting from atmospheric distillation of a crude oil, to any one or more treatments selected from solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, and hydrorefining; wax-isomerized mineral oils; and those produced by isomerizing GTL WAX (Gas to Liquid Wax) produced through Fischer-Tropsch process.

Specific examples of the synthetic base oil include polybutenes and hydrogenated compounds thereof; poly-α-olefins such as 1-octene oligomer and 1-decene oligomer, and hydrogenated compounds thereof; aromatic synthetic oils such as alkylnaphthalenes and alkylbenzenes; and mixtures of two or more of these oils.

The hydrocarbon solvent used in the present invention may be a mineral oil, a hydrocarbon synthetic oil or any mixture of two more types selected from these oils. For example, the solvent may be a mixture of more than one mineral oils, a mixture of more than one hydrocarbon synthetic oils, or a mixture of one or more mineral oil and one or more hydrocarbon synthetic oil.

The hydrocarbon solvent used in the present invention has a 100° C. kinematic viscosity of necessarily 0.5 to 4.5 mm²/s, preferably 1.0 to 4.3 mm²/s, more preferably 1.5 to 4.2 mm²/s, most preferably 2.0 to 4.1 mm²/s. A hydrocarbon solvent having a 100° C. kinematic viscosity of less than 0.5 mm²/s is not preferable with the objective of evaporation loss. A hydrocarbon solvent having a 100° C. kinematic viscosity of greater than 4.5 mm²/s is not also preferable because of its poor dissolubility of a metal salt of a phosphorus-containing compound.

The hydrocarbon solvent used in the present invention has a % C_(A) of necessarily 3 or less, preferably 2.5 or less, more preferably 2.0 or less, more preferably 1.5 or less. A hydrocarbon solvent having a % C_(A) of greater than 3 is not preferable because it tends to be reduced in dissolubility of a metal salt of a phosphorus-containing compound. The hydrocarbon solvent may have a % C_(A) of 0.

The % C_(A) used herein denote the percentages of the aromatic carbon number in the total carbon number, determined by a method (n-d-M ring analysis) in accordance with ASTM D 3238-85.

The hydrocarbon solvent used in the present invention has a sulfur content of necessarily 0.05 percent by mass or less, preferably 0.04 percent by mass or less, more preferably 0.03 percent by mass or less, particularly preferably 0.02 percent by mass or less. A hydrocarbon solvent having a sulfur content of more than 0.05 percent by mass is not preferable because it tends to be reduced in dissolubility of a metal salt of a phosphorus-containing compound.

Generally, the sulfur content of a hydrocarbon solvent varies on the sulfur content of its raw material. For example, in the case of using a raw material containing substantially no sulfur such as a synthetic wax produced through a Fischer-Tropsch reaction, a hydrocarbon solvent containing substantially no sulfur can be produced. In the case of using a raw material containing sulfur such as a slack wax produced through the refining process of a hydrocarbon solvent or a micro wax produced through wax refining, the sulfur content of the resulting hydrocarbon solvent is usually 0.01 percent by mass or more. In the present invention, the sulfur content is necessarily 0.05 percent by mass or less.

The sulfur content referred herein is measured in accordance with the method described in JIS K2541-1996.

No particular restriction is imposed on the viscosity index of the hydrocarbon solvent used in the present invention. However, the viscosity index is preferably 80 or greater, 100 or greater, most preferably 120 or greater such that excellent viscosity characteristics can be obtained at from low temperatures to high temperatures. No particular restriction is imposed on the upper limit of the viscosity index. Those with a viscosity index of 135 to 180 such as normal paraffins, slack waxes, GTL waxes or isoparaffin mineral oil produced by isomerizing them may be used. A hydrocarbon solvent with a viscosity index of less than 80 would tend to be reduced in dissolubility of a metal salt of a phosphorus-containing compound.

The additive composition for a lubricating oil of the present invention comprises the above-described hydrocarbon solvent and one or more metal salt of a phosphorus-containing compound represented by formula (1) below (hereinafter simply referred to as “a metal salt of a phosphorus-containing compound) in an amount of 10 to 90 percent by mass on the basis of the total mass of the composition.

In formula (1), X¹ and X² are each oxygen or sulfur. R¹, R², R³ and R⁴ are each independently a straight-chain alkyl group having 3 to 12, preferably 4 to 11, more preferably 4 to 10, most preferably 4 to 8 carbon atoms. An alkyl group having fewer than 3 carbon atoms would cause the resulting metal salt to be poor in dissolubility while an alkyl group having more than 12 carbon atoms would makes it difficult to produce the metal salt. The average carbon number of R¹, R², R³ and R⁴ is necessarily 5 or greater. M is a divalent metal atom, specific examples of which include zinc, copper, nickel, cobalt, calcium and magnesium. Preferred is zinc.

Examples of the straight-chain alkyl group include n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, and n-dodecyl groups.

Specific examples of the phosphorus-containing compound include di-n-butylphosphate, di-n-hexylphosphate, di-n-octylphosphate, di-n-decylphosphate, di-n-dodecylphosphate, n-butyl-n-hexylphosphate, n-butyl-n-octylphosphate, di-n-butylthiophosphate, di-n-hexylthiophosphate, di-n-octylthiophospahte, n-butyl-n-hexylthiophosphate, n-butyl-n-octylthiophosphate, and mixtures thereof.

Specific examples of the compounds represented by formula (1) include metal salts, such as zinc, copper, nickel, cobalt, calcium, and magnesium salts of the above-described phosphorus-containing compounds.

The mix ratio of the metal salt of the phosphorus-containing compound to the hydrocarbon solvent is from 10 to 90 percent by mass, preferably from 30 to 85 percent by mass, more preferably from 35 to 80 percent by mass, most preferably from 40 to 75 percent by mass on the basis of the total mass of the composition. When the mix ratio is less than 10 percent by mass, the amount of the additive to be added during the process of production of a lubricating oil would be increased, possibly causing an increase in the evaporation loss of the lubricating oil. When the mix ratio is more than 90 percent by mass, the additive would separate from the lubricating oil during the storage thereof.

The additive composition for a lubricating oil of the present invention has a 100° C. kinematic viscosity of preferably 0.5 to 4.5 mm²/s, more preferably 1.0 to 4.3 mm²/s, more preferably 1.5 to 4.2 mm²/s.

The additive composition of the present invention can be easily produced by, for example, adding a metal salt of a phosphorus-containing compound having been finely crushed, to a hydrocarbon solvent heated to a temperature of 30 to 60° C. and stirring the mixture at a revolution number of about 300 rpm or alternatively dissolving a metal salt of a phosphorous-containing compound in an organic solvent such as hexane and then mixing the metal salt with a hydrocarbon solvent, followed by removal of the organic solvent.

The resulting additive composition for a lubricating oil of the present invention is used as an additive for various lubricating oils.

EXAMPLES

The present invention will be described more specifically with reference to the following Examples and Comparative Examples but not limited thereto.

Examples 1 to 8, Comparative Examples 1 to 16

The following metal salts of phosphorous-containing compounds were added to the following hydrocarbon solvents to prepare additive compositions for lubricating oils (Examples 1 to 8, Comparative Examples 1 to 16) having formulations set forth in Tables 1 and 2 below. The hydrocarbon solvents and metal salts of phosphorous-containing compounds in the tables are as follows.

(1) Hydrocarbon Solvents

Solvent 1: Paraffinic solvent refined mineral oil (100° C. kinematic viscosity: 2.1 mm²/s, % C_(A): 5, sulfur content: 800 ppm by mass)

Solvent 2: Hydrogenated refined mineral oil (100° C. kinematic viscosity: 2.7 mm²/s, % C_(A): 0, sulfur content: 0 ppm by mass)

Solvent 3: Poly-α-olefin (PRO) (100° C. kinematic viscosity: 4.0 mm²/s, % C_(A): 0, sulfur content: 0 ppm by mass)

(2) Metal salts of phosphorus-containing compounds

Phosphorus compound A: zinc n-butyl-n-hexylphosphate (average carbon number: 5, phosphorus content: 11.5 percent by mass, zinc content: 11.9 percent by mass)

Phosphorus compound B: zinc di-n-hexylphosphate (average carbon number: 6, phosphorus content: 10.4 percent by mass, zinc content: 10.7 percent by mass)

Phosphorus compound C: zinc n-butyl-n-octylphosphate (average carbon number: 6, phosphorus content: 10.4 percent by mass, zinc content: 10.7 percent by mass)

Phosphorus compound D: zinc n-butyl-n-octylthiophosphate (average carbon number: 6, phosphorus content: 9.8 percent by mass, zinc content: 10.1 percent by mass, sulfur content: 10.1 percent by mass)

Phosphorus compound F: zinc di-n-butylphosphate (average carbon number: 4, phosphorus content: 12.8 percent by mass, zinc content: 13.1 percent by mass)

Phosphorus compound F: zinc di-n-butylthiophosphate (average carbon number: 4, phosphorus content: 11.9 percent by mass, zinc content: 12.3 percent by mass, sulfur content: 12.3 percent by mass)

Phosphorus compound G: zinc n-butyl-n-hexylphosphate (average carbon number: 4.5, phosphorus content: 12.2 percent by mass, zinc content: 12.6 percent by mass)

Phosphorus compound H: zinc di-2-ethylhexylphosphate (phosphorus content: 8.8 percent by mass, zinc content: 9.1 percent by mass)

Phosphorus compound I: zinc di-2-ethylhexyldithiophosphate (phosphorus content: 8.4 percent by mass, zinc content: 8.7 percent by mass, sulfur content: 8.7 percent by mass)

The additive compositions for a lubricating oil of Examples 1 to 8 and Comparative Examples 1 50 16 were subjected to a storage test at normal temperature to observe whether they were liquefied at a temperature of 60° C. and whether insoluble precipitated after 1 week, 2 weeks, 3 weeks and 4 weeks. The results are set forth in Tables 1 and 2. A stable additive composition for a lubricating oil cannot be produced in the case of using solvent 1 not having the properties defined by the present invention and phosphorus-containing compounds having a branched alkyl group.

TABLE 1 Test Oil No. 1 2 3 4 5 6 7 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Solvent 1 mass % — — — — — — — Solvent 2 mass % balance — balance — balance — balance Solvent 3 mass % — balance — balance — balance — Phosphorus Compound A mass % 50 50 — — — — — Phosphorus Compound B mass % — — 50 50 — — — Phosphorus Compound C mass % — — — — 50 50 — Phosphorus Compound D mass % — — — — — — 50 Phosphorus Compound E mass % — — — — — — — Phosphorus Compound F mass % — — — — — — — Phosphorus Compound G mass % — — — — — — — Phosphorus Compound H mass % — — — — — — — Phosphorus Compound I mass % — — — — — — — Average Carbon Number  5  5  6  6  6  6  6 of Phosphorus Compound Liquefaction at 60° C. Yes Yes Yes Yes Yes Yes Yes Stability at room one week No No No No No No No temperature (Insoluble) two weeks No No No No No No No three weeks No No No No No No No four weeks No No No No No No No Test Oil No. 9 10 11 12 8 Comparative Comparative Comparative Comparative Example 8 Example 1 Example 2 Example 3 Example 4 Solvent 1 mass % — balance balance balance balance Solvent 2 mass % — — — — — Solvent 3 mass % balance — — — — Phosphorus Compound A mass % — 50 — — — Phosphorus Compound B mass % — — 50 — — Phosphorus Compound C mass % — — — 50 — Phosphorus Compound D mass % 50 — — — 50 Phosphorus Compound E mass % — — — — — Phosphorus Compound F mass % — — — — — Phosphorus Compound G mass % — — — — — Phosphorus Compound H mass % — — — — — Phosphorus Compound I mass % — — — — — Average Carbon Number  6  5  6  6  6 of Phosphorus Compound Liquefaction at 60° C. Yes Yes Yes Yes Yes Stability at room one week No No No No No temperature (Insoluble) two weeks No Yes No Yes Yes three weeks No Yes Yes Yes Yes four weeks No Yes Yes Yes Yes

TABLE 2 Test Oil No. 13 14 15 16 17 18 19 Comparative Comparative Comparative Comparative Comparative Comparative Comparative Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Solvent 1 mass % — — — — — — — Solvent 2 mass % balance — balance — balance — balance Solvent 3 mass % — balance — balance — balance — Phosphorus Compound A mass % — — — — — — — Phosphorus Compound B mass % — — — — — — — Phosphorus Compound C mass % — — — — — — — Phosphorus Compound D mass % — — — — — — — Phosphorus Compound E mass % 50 50 — — — — — Phosphorus Compound F mass % — — 50 50 — — — Phosphorus Compound G mass % — — — — 50 50 — Phosphorus Compound H mass % — — — — — — 50 Phosphorus Compound I mass % — — — — — — — Average Carbon Number  4  4  4  4   4.5   4.5  8 of Phosphorus Compound Liquefaction at 60° C. Yes Yes No No Yes Yes No Stability at room one week Yes Yes Yes Yes temperature (Insoluble) two weeks three weeks four weeks Test Oil No. 20 21 22 23 24 Comparative Comparative Comparative Comparative Comparative Example 12 Example 13 Example 14 Example 15 Example 16 Solvent 1 mass % — — — balance balance Solvent 2 mass % — balance — — — Solvent 3 mass % balance — balance — — Phosphorus Compound A mass % — — — — — Phosphorus Compound B mass % — — — — — Phosphorus Compound C mass % — — — — — Phosphorus Compound D mass % — — — — — Phosphorus Compound E mass % — — — 50 — Phosphorus Compound F mass % — — — — — Phosphorus Compound G mass % — — — — — Phosphorus Compound H mass % 50 — — — 50 Phosphorus Compound I mass % — 50 50 — — Average Carbon Number  8  8  8  4  8 of Phosphorus Compound Liquefaction at 60° C. No No No Yes No Stability at room one week Yes No temperature (Insoluble) two weeks three weeks four weeks

INDUSTRIAL APPLICABILITY

The additive composition for a lubricating oil of the present invention is significantly large in industrial value because it can be produced at a relatively low temperature, which is 60° C. or lower for a short period of time, does not have any adverse effect such as causing rubber seals to swell, and is excellent in storage stability. 

1. An additive composition for a lubricating oil, comprising a metal salt of a phosphorus-containing compound represented by formula (1) in an amount of 10 to 90 percent by mass on the basis of the composition, contained in a hydrocarbon solvent selected from a mineral oil, a hydrocarbon synthetic oil and a mixture thereof, the hydrocarbon solvent having a 100° C. kinematic viscosity of 0.5 to 4.5 mm²/s, a % C_(A) of 3 or less, and a sulfur content of 0.05 percent by mass or less:

wherein X¹ and X² are each independently oxygen or sulfur, R¹, R², R³, and R⁴ are each independently a straight-chain alkyl group having 3 to 12 carbon atoms, the average of the carbon number is 5 or greater, and M is a divalent metal atom.
 2. A process for producing an additive composition for a lubricating oil, comprising dissolving a metal salt of a phosphorus-containing compound represented by formula (1) in an amount of 10 to 90 percent by mass on the basis of the composition in a hydrocarbon solvent selected from a mineral oil, a hydrocarbon synthetic oil and a mixture thereof, the hydrocarbon solvent having a 100° C. kinematic viscosity of 0.5 to 4.5 mm²/s, a % C_(A) of 3 or less, and a sulfur content of 0.05 percent by mass or less:

wherein X¹ and X² are each independently oxygen or sulfur, R¹, R², R³, and R⁴ are each a straight-chain alkyl group having 3 to 12 carbon atoms, the average of the carbon number is 5 or greater, and M is a divalent metal atom.
 3. A lubricating oil composition comprising the additive composition for a lubricating oil according to claim
 1. 